The invention relates generally to a power converter system and more specifically to an AC to DC step down power converter system.
Power converters are used in a wide variety of applications. Equipment such as UPS's, battery chargers, AC-DC power supplies and others use an AC-DC power converter to convert incoming AC, typically from a power grid, to DC power output. Typically, techniques such as PWM (pulse width modulation) boost conversion have been successfully deployed to produce AC-DC power converters with high power factor and sinusoidal input currents. However the DC voltage in such cases is higher than the peak value of the AC supply (boost function). In a wide variety of applications, such as those mentioned above, the DC voltage required is usually lower than the peak value of the AC supply (step down function).
Current techniques and devices employed for achieving a AC-DC step down function, such as thyristor controlled rectifiers, input step down transformers, additional DC-DC power conversion circuits and others have a low power factor and inject harmonics into the AC source. Generally, an additional power factor correction stage may be incorporated in such power converters. Two stage power converters combining the power factor correction stage, with a down converter stage, are typically used when high efficiency and low input current harmonics are required. However, typical two stage power converters are costly for low power applications. In addition, compliance to standards, such as IEEE 519, requires additional equipment that is expensive, bulky and generally reduces the overall efficiency of the system. Hence, present methods have limitations for achieving high level of power factor and low harmonic performance for AC-DC step down function and tend to be expensive and less efficient.
It is therefore desirable to provide a cost-effective and efficient AC-DC step down power converter having high power factor and a low level of input current harmonics.